1. Field of the Invention
The invention relates to a composite electrolyte membrane, membrane-electrode assembly, a fuel cell, and methods for manufacturing same, and more particularly to a composite electrolyte membrane having at least an electrolyte layer composed of an electrolyte and a reinforcing layer in which a porous polymer material is impregnated with the electrolyte, a membrane-electrode assembly, a fuel cell, and methods for manufacturing same.
2. Description of the Related Art
Solid polymer fuel cells using an electrolyte membrane have been studied for applications to movable bodies such as automobiles because such fuel cells may operate at a low temperature and have small size and weight. In particular, social interest in fuel cell automobiles having solid polymer fuel cells installed thereon as ecological cars has been growing.
As shown in FIG. 14, a solid polymer fuel cell has a membrane-electrode assembly (MEA) 95 as the main structural element. A single fuel cell 90, which is called a unit cell, is formed by sandwiching the membrane-electrode assembly between separators 96 having a fuel (hydrogen) gas flow channel and an air gas low channel. The membrane-electrode assembly 95 has a structure in which an anode-side electrode (anode catalyst layer) 93a is laminated on one side of an electrolyte membrane 91 that is an ion exchange membrane and a cathode-side electrode (cathode catalyst layer) 93b is laminated on the other side, and respective diffusion layers 94a, 94b are disposed at the anode catalyst layer 93a and cathode catalyst layer 93b. 
In order to ensure the membrane strength, the electrolyte membrane 91 is provided with a reinforcing layer composed of a porous polymer material such as polytetrafluoroethylene (PTFE), and the reinforcing layer is impregnated with an electrolyte. Such a composite electrolyte membrane having a reinforcing layer is manufactured by a cast film forming method illustrated by FIG. 13A, which is disclosed in Japanese Patent Application Publication No. 2006-147257 (JP-A-2006-147257).
More specifically, first, an electrolyte including an electrolyte polymer and a solvent is coated on one side of a backing sheet 81 that is being transported, and the electrolyte is dried. Then, a reinforcing sheet 82 composed of a porous polymer material is disposed on the surface of the dried electrolyte layer. The electrolyte is impregnated from one surface of the reinforcing sheet 82 into the porous polymer materials at least by applying pressure to the electrolyte layer and reinforcing sheet 82 in this disposition state. Then, the electrolyte is coated on the other surface of the reinforcing sheet 82 and dried thereby making it possible to manufacture the composite electrolyte membrane 91 in which at least the reinforcing layer composed of the porous polymer material and the electrolyte impregnated in the reinforcing layer are provided on the backing sheet 81.
In the composite electrolyte membrane 91 manufactured in the above-described manner, as shown in FIG. 13B, for example, the anode catalyst layer 93a and cathode catalyst layer 93b that have been formed on the backing sheet 81 are transferred by using a tool and employing heating and pressure application, and catalyst layers 93a, 93b are further formed on the surface of the composite electrolyte membrane 91.
However, in the above-described cast film forming method, the electrolyte is impregnated in two surfaces of the reinforcing sheet in different processes. As a result, although the same electrolyte containing an electrolyte polymer and a solvent is used, a spread in film properties may occur between the two surface sides of the composite electrolyte membrane and uniform properties are difficult to obtain.
Further, because the manufacturing process includes coating the electrolyte on each surface and drying the solvent, an electrolyte membrane having a highly accurate uniform film thickness is sometimes difficult to obtain. In addition, the position of the reinforcing sheet with respect to the coated electrolyte may be displaced from the desired position correspondingly to the accuracy of the manufacturing apparatus. This displacement especially easily occurs in the arrangement of anode and cathode catalyst layers.
Thus, when uniform membrane properties are not obtained on both surfaces of the electrolyte membrane and when the thickness of the electrolyte membrane and positions of catalyst layers are not within the desired accuracy ranges, defective assembling may occur in the cell manufacturing process or a spread may occur in the fuel cell performance during power generation.